Corrosion evolution of aluminium-copper and aluminium-copper-lithium alloys in chloride solution

The objective of this work is to better understand the corrosion behavior of AA2024 (aluminium-copper) and AA2050 (aluminium-copper-lithium) alloys – used in aircraft fuselage and wings – by following their reactivity in a low-aggressive electrolyte (NaCl 0.01 M) using electrochemical and surface science techniques. It is shown that pitting is the predominant mode of corrosion, initiated at the locations where intermetallic particles were torn off from the surface during polishing. By using surface characterization techniques, a growing corrosion product layer mainly composed of oxidized aluminium was followed during 72 h of immersion in the electrolyte. It is revealed that lithium increases the alloy’s thermodynamic susceptibility to corrosion but leads to reduction of the kinetic corrosion rate by promoting the formation of a more homogeneous corrosion product layer. Additionally, it is shown that the mechanism evolves over time. During the first hours of immersion, the limiting reaction is the charge transfer between the metallic substrate and the electrolyte while for longer immersion times, it becomes the diffusion of the dissolved dioxygen from the electrolyte in the growing oxide layer.